Bituminous composite elements

ABSTRACT

The invention relates to composite elements which have the following layer structure:  
     (i) from 2 to 20 mm of metal, plastic or wood,  
     (ii) from 10 to 300 mm of mixture comprising bitumen,  
     (iii) from 2 to 20 mm of metal, plastic or wood.

[0001] The invention relates to composite elements which have the following layer structure:

[0002] (i) from 2 to 20 mm, preferably from 3 to 10 mm, particularly preferably from 5 to 10 mm, of metal, wood, or plastic, such as polyethylene, polypropylene, ABS, thermoplastic polyurethane, ASA, or PVC, preferably metal,

[0003] (ii) from 10 to 300 mm, preferably from 10 to 100 mm, of mixture comprising bitumen,

[0004] (iii) from 2 to 20 mm, preferably from 3 to 10 mm, particularly preferably from 5 to 10 mm, of metal, wood, or plastic, such as polyethylene, polypropylene, ABS, thermoplastic polyurethane, ASA, or PVC, preferably metal.

[0005] The invention further relates to processes for producing these composite elements, and their use.

[0006] The structural components used in the design of ships, for example hulls and cargo hold covers, or bridges, roofs, or multistorey buildings, have to be able to withstand considerable stresses from external forces. Due to these requirements, structural components of this type are usually composed of metal plates or metal supports, strengthened by appropriate geometry or suitable struts. Due to increased safety standards, tanker hulls are therefore usually composed of an inner and an outer hull, each hull being built up from steel plates of 15 mm thickness, connected to one another via steel struts about 2 m in length. Since these steel plates are exposed to considerable forces, both the outer and the inner steel shells are reinforced by welded-on reinforcing elements. Disadvantages of these traditional structural components are firstly the considerable amounts of steel required and secondly the time-consuming and labor-intensive method of manufacture. Structural components of this type also have considerable weight, reducing the ship's tonnage and increasing fuel consumption. In addition, structural components of this type based on steel also require heavy maintenance, since both the outer surface and the surfaces of the steel components between the outer and inner shells regularly have to be provided with corrosion protection.

[0007] Known substitutes for designs based on steel are SPS elements (Sandwich plate systems), comprising a composite made from metal and plastic, usually polyisocyanate polyaddition products. The adhesion of the plastic to the two metal layers produces composite elements with remarkable advantages over known designs based on steel. U.S. Pat. No. 6,050,208, U.S. Pat. No. 5,778,813, DE-A 198 25 083, DE-A 198 25 085, DE-A 198 25 084, DE-A 198 25 087 and DE-A 198 35 727 disclose SPS elements of this type.

[0008] An important characteristic of the synthetic elastomeric polymer in the SPS is its high-temperature properties together with its processability and its cost-effectiveness.

[0009] It is an object of the present invention, therefore, to develop novel composite elements which have good heat resistance, are easy to use and install, and are also inexpensive to produce.

[0010] We have found that this object is achieved by the composite elements described at the outset.

[0011] For the purposes of the present invention, bitumen is a low-volatility mixture obtained from the treatment of crude oil and comprising various organic substances, and having viscoelastic behavior which changes with temperature. Other definitions of bitumens are given in Rompp Chemie Lexikon, 9^(th) revised edition, Georg Thieme Verlag, Stuttgart, New York, and in particular in DIN 55 946 Part 1, which is decisive in case of doubt. Bitumens are well known and various types of these are commercially available. An example of information concerning bitumen, the various types, additives, processing and handling are found in “Shell Bitumen für den Straβenbau und andere Anwendungsgebiete”, 7^(th) edition, 1994, Deutsche Shell Aktiengesellschaft, Hamburg and “The Shell Bitumen Industrial Handbook” published by Shell Bitumen, Chertsey, Surrey, UK, 1995 (ISBN-0-95 16625-1-1).

[0012] In principle, any of the types of bitumen may be used for the application of the invention in the composite elements. Taking into account the various applications and possible production processes for the composite elements, it can be advantageous to select those products from the bitumens which are known and have been described which are advantageous in respect of softening point, viscosity at usage temperature, adhesion to layers (i) and (iii), and also elastic properties. This selection or the possibility of matching bitumen or bitumen mixtures is a familiar matter to the skilled worker in the sector. For example it can be advantageous for composite elements exposed to particularly high thermal stress to use bitumens which have a high softening point.

[0013] Bitumen to DIN 55 946 Part 1 with a needle penetration to DIN 52010 of from 0.1 to 80 mm is preferably used as (ii).

[0014] Preference is moreover given to composite elements comprising bitumen with a softening point to DIN 52011 of at least 500C, preferably at least 80° C.

[0015] Preference is also given to composite elements comprising bitumen with a content of from 8 to 30% by weight of asphaltenes.

[0016] Preference is also given to composite elements comprising oxidation bitumen. This oxidation bitumen can be produced by known processes, and is commercially available.

[0017] The composite elements may preferably comprise, as layer (ii) between layers (i) and (iii), bitumen in a mixture with inorganic fillers and/or with plastics. The advantages of appropriate additives for the properties of the bitumen mixture are well known and have been widely described. Using the known properties of the mixtures, therefore, the skilled worker can use an advantageous blend for any of a very wide variety of applications for the composite elements, for example one appropriate for the mechanical or thermal stress.

[0018] A material which may preferably be used as (ii) is bitumen in a mixture with SBS (styrene-butadiene-styrene), SBR (styrene-butadiene rubber), SIS (styrene-isoprene-styrene), EPDM (ethylene-propylene-diene rubber), ethylene-butyl acrylate, ethylene-vinyl acetate (EVA), ethylene-methyl acrylate, and/or polyolefins, such as polyethylene, polypropylene, ethylene-propylene copolymers. Bitumens in mixtures with these plastics have been widely described and are generally familiar to the skilled worker. Plastics suitable as additives are marketed y Elenac GmbH, Germany, for example, with the trademark Lucobit®. The plastics, in particular the polyolefins, preferably ave a number-average molar mass of from 20 000 to 1 000 000 g/mol. The content of plastics in the mixture with bitumen may usually be from 0 to 30% by weight, preferably from 0 to 13% by weight, based in each case on the total weight of (ii). or the purposes of the present invention, examples of inorganic fillers are gypsum, barium sulfate, sand, cement and/or rock lour. These inorganic additives are widely described and well known as additives for bitumen. Their particle size is usually from 1 to 75 μm, or in the case of sand usually from 0.08 to 2 mm. However, where appropriate use may also be made of larger particles, such as chippings known for this purpose with a grain size of at least 4 mm, preferably from 4 to 10 mm. The content of inorganic fillers in the mixture with bitumen may usually be from 0 to 90% by weight, preferably from 0 to 50% by weight, based in each case on the total weight of (ii).

[0019] In addition to the stated additives for the bitumen, use may also be made of fibers well known for this purpose, such as glass fibers, cellulose and/or rock fiber, and/or further known additives, such as dyes, oils, waxes, or fats. Examples of descriptions of possible additives and their use with bitumen are described in DE-A 199 03 314, EP-A 1 008 630 and U.S. Pat. No. 6,133,350.

[0020] Bitumen is usually mixed with the stated possible other constituents at from 140 to 240° C, this temperature preferably being selected as a function of the bitumen used and of the additives desired. The mixing may take place by well known methods, depending on the additive.

[0021] Mixtures of bitumen with the stated additives have been widely described and a very wide variety of types of these are commercially available.

[0022] Preference is given to composite elements which have the following layer structure:

[0023] (i) from 2 to 20 mm, preferably from 3 to 10 mm, particularly preferably from 5 to 10 mm, of metal,

[0024] (ii) from 10 to 300 mm, preferably from 10 to 100 mm, of bitumen,

[0025] (iii) from 2 to 20 mm, preferably from 3 to 10 mm, particularly preferably from 5 to 10 mm, of metal.

[0026] In this preferred embodiment, the term “bitumen” also means mixtures comprising bitumen and other constituents well known in mixtures with bitumen, for example the additives described at the outset.

[0027] One way of producing the composite elements of the invention is to introduce, between the layers (i) and (iii), a mixture comprising bitumen, usually softened or molten bitumen, preferably at a bitumen temperature of from 140 to 240° C. In order to prevent any undesired premature cooling and thus hardening of the bitumen between (i) and (iii) before the entire space to be filled has been filled between (i) and (iii), it can be advantageous to heat the layers (i) and (iii) prior to and/or during the introduction of the bitumen, preferably to 40-2400C, particularly preferably 60-150° C. This particularly applies when the layers (i) and (iii) are composed of metal, since metals have high heat capacity and when cold could rapidly cool the hot bitumen.

[0028] An example of the production of the composite elements is a process in a closed mold, that is to say that the location of (i) and (iii) prior to filling with (ii) is in a mold which is sealed once introduction of (ii) has been completed. The composite element can be removed from the mold after (ii) has hardened.

[0029] In one example, (i) and (iii) may be secured in a suitable arrangement, for example parallel to one another. The separation selected is usually such to give a space of thickness of from 10 to 300 mm between (i) and (iii). An example of a way of securing (i) and (iii) is by way of spacers. It is preferable for the edges of the intervening space to be sealed off in a way which allows the space between (i) and (iii) to be filled with (ii) but which prevents the components from escaping. The sealing-off process may use the usual plastics films or metal foils, and/or metal plates, and these may also serve as spacers.

[0030] Either a vertical or a horizontal orientation of (i) and (iii) may be used for filling the space between (i) and (iii) with (ii).

[0031] The usual equipment for conveying or pouring hot bitumen, preferably continuously, may be used for filling the space between (i) and (iii) with (ii). Depending on the viscosity of (ii) during the filling process, (ii) may be simply poured, or else injected under pressure. It is preferable for the filling of the space between (i) and (iii) to have been entirely completed before (ii) hardens.

[0032] Another process for producing the composite elements consists in applying molten or softened (ii) to the surface of (i) and then securing (iii) to the molten or softened (ii). For example, the mixture comprising bitumen, molten or softened, may be calendered, troweled, or spread onto (i). The layer (iii) may then be brought into contact with (ii) and preferably secured in the desired position until (ii) has hardened. A uniformly thick layer (ii) is a possible and preferred objective when (ii) is applied to (i), the thickness depending on the desired dimensions of the composite element. Excess bitumen may flow out or be extruded at the margin or at prepared openings in (i) and/or (iii).

[0033] An alternative consists in prefabricating a layer (ii) and adhesively bonding this, for example, while it is solid to (i) and (iii). This process in which (ii) is adhesively bonded to (i) and (iii) may be carried out using adhesives well known for these materials. Simple routine experiments may be used by the skilled worker to discover a selection of suitable adhesives.

[0034] It is preferable for those surfaces of (i) and/or (iii) to which (ii) adheres once the composite elements have been produced to be blasted with sand or with steel shot. Usual processes may be used for this sand blasting. For example, the usual sand may be used to sand blast the surfaces at high pressure, thus, for example, cleaning and roughening the surfaces. Suitable equipment for treatment of this type is commercially available.

[0035] This treatment of those surfaces of (i) and (iii) which are in contact with (ii) once (a) has been reacted with (b) can give markedly improved adhesion of (ii) to (i) and (iii). The sand blasting is preferably carried out directly prior to introduction of the components for producing (ii) into the space between (i) and (iii). The surfaces to which (ii) is to adhere on (i) and (iii) are preferably free from inorganic and/or organic substances which reduce adhesion, for example oils or fats, or generally any substance known to be a mold-release agent.

[0036] The layers (i) and (iii) used, usually sheets, may preferably be conventional metals, such as iron, conventional steel, any type of refined steel, aluminum, and/or copper.

[0037] Either (i) or (iii) may have been coated, for example primed, painted, and/or coated with conventional plastics, before use to produce the composite elements of the invention. It is preferable for (i) and (iii) not to have been coated, and it is particularly preferable for these to have been cleaned, for example by conventional sand blasting, before their use.

[0038] The composite elements of the invention are used primarily in sectors which require structural components which withstand large forces, for example as structural components in shipbuiling, e.g. in ships' hulls, such as ships' double hulls with an outer and an inner wall, or in cargo hold covers, cargo hold partitions, or cargo doors, or in civil engineering works, such as bridges, or as structural components in the construction of buildings, in particular for multistorey buildings.

[0039] Advantages of the composite elements of the invention over known composite elements for the same applications are to be found in the heat resistance of suitable bitumens, in simple handling, including during the installation of the composite elements, and in cost-effective production. 

We claim:
 1. A composite element which has the following layer structure: (i) from 2 to 20 mm of metal, plastic or wood, (ii) from 10 to 300 mm of mixture comprising bitumen, (iii) from 2 to 20 mm of metal, plastic or wood.
 2. A composite element as claimed in claim 1 comprising, as (ii), bitumen in a mixture with inorganic fillers and/or with plastics.
 3. A composite element as claimed in claim 1, comprising, as (ii), bitumen in a mixture with SBS, SBR, SIS, EPDM, polyolefins, ethylene-butyl acrylate, ethylene-vinyl acetate and/or ethylene-methyl acrylate.
 4. A composite element as claimed in claim 1, comprising bitumen to DIN 55 946 Part 1 with needle penetration to DIN 52 010 of from 0.1 to 80 mm.
 5. A composite element as claimed in claim 4, comprising bitumen with a softening point to DIN 52011 of at least 50° C.
 6. A composite element as claimed in claim 1, comprising bitumen with a content of from 8 to 30% of asphaltenes.
 7. A composite element as claimed in claim 1, comprising oxidized bitumen.
 8. A process for producing composite elements as claimed in claim 1, which comprises introducing a mixture comprising molten or softened bitumen between the layers (i) and (iii).
 9. A process for producing composite elements as claimed in claim 1, which comprises applying molten or softened (ii) to the surface of (i) and then securing (iii) to the molten or softened (ii).
 10. A process for producing composite elements as claimed in claim 1, which comprises adhesively bonding (ii) to (i) and (iii).
 11. A ship or an item of civil engineeering work comprising composite elements as claimed in any of claims 1 to
 7. 